Vertical lifts such as wheelchair lifts for disabled persons are well-known. Representative of known wheelchair lifts is U.S. Pat. No. 3,661,228 of Glasser issued May 9, 1972 which describes and illustrates a screw driven platform which is selectively adjustable to a lowered wheelchair loading and unloading position and a raised curb position. A manually operable toe plate serves as a ramp, when in lowered position, and an obstruction to confine the wheelchair to the platform when in raised position. The platform is raised and lowered by means of a pair of screw drives seated within tubular housings. They drive a pair of C-shaped traveller brackets which are directly secured to a beam which is part of the frame structure of the lift platform. Controls for the platform are permanently mounted near the motor.
Other wheelchair lift constructions are described and illustrated in U.S. Pat. Nos. 4,133,437 of Gates issued Jan. 9, 1979; 4,281,744 of Koerber issued Aug. 4, 1981 and 4,283,803 of Krumbeck issued Aug. 18, 1981 and European Patent Application of David Paul Erlam, et al published under EP 0 739 852 A2 on Oct. 30, 1996.
Other references of background interest relating generally to screw driven elevators include Canadian Patent No. 291,699 issued Jul. 30, 1929 of Kreutzkamp and U.S. Pat. Nos. 3,468,401 of Letz issued Sep. 23, 1969, 2,527,897 of Todd issued Oct. 31, 1950 and 4,919,236 of Karisson et al issued Apr. 23, 1990
Of background interest relating to switch actuators for incapacitated persons or otherwise include U.S. Pat. Nos. 2,486,591 of Ferrante issued Nov. 1, 1949; 2,828,379 of Simonds et al issued Mar. 25, 1958; 3,935,410 of Howard issued Jan. 27, 1976; 4,306,132 of Henville issued Dec. 15, 1981; 4,172,217 of Miller issued Oct. 23, 1979, as well as Canadian Patent No. 637,165 of Holden issued Feb. 27, 1962.
Most of these known lifts for disabled persons and persons in wheelchairs, as well as the previously described lifts, appear to be extremely complex in construction and hence expensive to build. Many of these constructions are suitable for an indoor location but would be completely inadequate for an exterior location where rain, snow, ice, leaves and other things may seriously hamper their effective operation.
It is thus an object of the present invention to provide a vertical lift for use by disabled persons and others, that is suitable for use in exterior locations, and which is economical to make and both reliable and secure in operation. It is a further object of the present invention to provide such a lift which is simple to put in place or remove. It is yet a further object of the present invention to provide such a lift which is both easy and safe for a disabled person to operate.